As much as I like Apple's GUI aesthetics - Quartz's font rendering is an absolute deal breaker for me. I much prefer the way fonts look with Microsoft's ClearType subpixel rendering (after proper tuning of course). That is for every-day stuff like web browsing and email that involves a lot of reading.

In situations where I need an accurate representation of what a typeface will look like in print, it's most likely in an application that has its own rendering engine anyway - InDesign in my case. Adobe's engine is called CoolType and produces results quite similar to those of Quartz as far as I can tell.